Introduction: Severely injured trauma patients (ISS > 16) are often mechanically ventilated for several days. 40% of them show a contusion of the lungs. Prolonged mechanical ventilation results in an increased risk for v

Introduction: Severely injured trauma patients (ISS > 16) are often mechanically ventilated for several days. 40% of them show a contusion of the lungs. Prolonged mechanical ventilation results in an increased risk for ventilator associated pneumonia (VAP). At the same time healing of lung tissue takes place. This circumstance makes it difficult to initiate a timely antiinfective therapy when VAP is suspected. At present no validated parameter or score exists, that allows a definitive discrimination between infection and inflammation. Triggering receptor on myeloid cells (TREM-1) is a receptor of the innate immune response system, described first in 2000. Its soluble part, sTREM-1, is significantly increased in the bronchoalveolar lavage (BAL) samples of patients with pneumonia (> 200pg/ml). No data regarding about sTREM-1 in patients who suffered lung contusion. As a consequence it is unclear whether sTREM-1 is a suitable marker for pneumonia in lung contusion. Material and methods: After approval of the local ethics committee and informed consent of the patients legal guardian, we enrolled 42 patients with thoracic trauma. On the first (Median 15 hours after trauma) and on the 2nd, 3rd, 5th, 6th and 7th day of ICU-treatment we collected BAL with an Aero-Jet catheter via the breathing tube (20 ml rinsing) and serum-probes at the same time. sTREM-1 levels were determined by enzyme-linked immunosorbent assay with repeated measurements (Quantikine sTREM-1 Immunoassay; R&D Systems). Serum-levels of interleukin (IL) 6 and 10 as well as lipopolysaccharid binding protein (LBP) were quantified by Immulite® (Siemens Medical Solution Diagnostics). The diagnosis of pneumonia was confirmed retrospectively by the Clinical Pulmonary Infection score (CPIS): Pneumonia = CPIS > 6; no pneumonia = CPIS &#8804; 6. Results and discussion: 15 hours after trauma the median sTREM-1 level in the BAL samples, in patients with clinical unremarkable course, was determined at 219pg/ml. Subsequently, after another 24h the median sTREM-1 level increased to a concentration of 575pg/ml and showed a similar concentration during the entire observation period. Patients with severe lung contusion showed increased sTREM-1 concentrations in BAL samples. The severity of lung contusion correlates with the amount of sTREM-1 level in BAL samples 40h after trauma. sTREM-1 concentration in patients with severe lung contusion (median 2240pg/ml) was significantly higher compared to patients without contusion (median 217pg/ml) or mild contusion (339pg/ml). On the day of diagnosis of pneumonia (CPIS > 6; n = 9), patients involved showed a significantly increased sTREM-1 level in the BAL sample (median 2145pg/ml; p < 0,05) in comparison to the day before pneumonia was diagnosed (median 588pg/ml). If the cut off is defined at 800pg/ml, the sensitivity is 87% and the specifity is 38%. In comparison to a negative BAL sample, a positive BAL sample shows a significantly higher sTREM-1 level (median 1492pg/ml vs. 971pg/ml; p < 0,05). Thus, the sensitivity (85%) is high, but the specifity (51%) is low. sTREM-1 is not only stimulated by infection, but also by tissue damage with bleeding and inflammation. sTREM-1 is due to contusion-caused stimulation in the first week after trauma and therefore not able to differentiate reliably between pneumonia an contusion-related inflammation. Cytokines and acute phase proteins (IL-6, IL-10, Procalcitonin) are also known to be unable to detect reliably an infection. A combination with sTREM-1 shows comparable results for sensitivity and specifity in the diagnosis of pneumonia as with the CPIS, whereas the CPIS can only be calculated retrospectively. The laboratory parameters are already present on the day of suspected infection. The clinical decision to initiate an antiinfective therapy correlated neither with the CPIS nor with the inflammation-parameters. Three of nine patients received no antiinfective therapy despite of increasing inflammation signs and a CPIS > 6. Consequently we feel that a combination of IL-6 and LBP in serum, sTREM-1 in BAL and CPIS clinical parameters can be helpful in making an informed decision for an antiinfective therapy in patients after polytrauma with suspected VAP.